Doing compression test on boat I want to purchase...question about test

[thepotroast]

I did a search on here and found a mass amount of info regarding compression testing. This is a Renken 17' open bow with a Mercruiser 3.0L, both are 1988's. I am going to look at the boat tomorrow and want to perform a compression test on it.

I am reading that the "lanyard kill switch" needs to be disconnected, what is this and where would I disconnect it from? This will be my first boat to own, but I grew up around boats. A lot of the terms are still new to me. I have done compression tests on other motors, I just don't want to screw up the ignition on this boat.

I think I have the other steps correct...after disconnecting this lanyard kill switch...

Make sure engine is warm first
Take out all spark plugs
Put compression gauge into each plug hole
Throttle open to full
Turn motor 6-8 cranks per cylinder
Compare readings...all should be over 100psi and should be within 10% of each other

This is a craigslist boat, paying it's worth price (considering NADA values and what other comparible boats in my area cost), and it really looks to be a great boat. I just don't want to get stuck with a bunk engine.

Any advice is appreciated.

 

[achris]

Re: Doing compression test on boat I want to purchase...question about test

The lanyard kill switch is (usually) on the control box. On Mercs it's a big silver toggle switch. Here's the thing, most I/Os don't have them connected. But you do have to 'disable' the ignition system, even when you open the lanyard switch. The easiest way is to pull the high tension lead from the centre of the dissy and jam it onto the block (or any other grounded metal). Then you don't need to bother with the lanyard switch.

Cheers,

Chris.............

 

[Zackman]

Re: Doing compression test on boat I want to purchase...question about test

You may find Mercruiser Service Bulletin 97-25 useful, here's a link http://www.boatfix.com/merc/Bullet/97/97_25.pdf​

 

[thepotroast]

Re: Doing compression test on boat I want to purchase...question about test

The easiest way is to pull the high tension lead from the centre of the dissy and jam it onto the block (or any other grounded metal). Then you don't need to bother with the lanyard switch.

So just take the wire running from the center of the dist cap and put the other end to the block on a grounded surface then?

 

[thepotroast]

Re: Doing compression test on boat I want to purchase...question about test

You may find Mercruiser Service Bulletin 97-25 useful, here's a link http://www.boatfix.com/merc/Bullet/97/97_25.pdf​

Thank you for the link! I will print this out and bring it with me!